Decarboxylation reaction
When sodium salt of a monocarboxylic acid is heated with soda lime (a mixture of NaOH and Cao in the ratio of 3:1) at about 630 K, alkane is formed.
RCOONa + NaOH -->RH + Na2CO3
In this reaction a CO2 group is removed from carboxylic acid and therefore the reaction is called decarboxylation.
Showing posts with label Preparation. Show all posts
Showing posts with label Preparation. Show all posts
Monday, January 28, 2008
Revision Alkenes - Methods of Preparation
From
alkynes
alkyl halides
dihalogen derivatives (dihalides)
alcohols
potassium salts of dicarboxylic acids
1. Partial reduction of alkynes
Alkynes can be reduced to alkenes using palladium-charcoal catalyst in catalytic hydrogenation (addition of hydrogen). The reduction (addition of hydrogen) can also be done using sodium in liquid ammonia.
2. Dehydrohalogenation of alkyl halides.
From alkyl halides, an atom of hydrogen and an atom of halogen are removed by treating it with alcoholic KOH.
As a hydrogen atom and a halogen atom are removed from the molecule, the reaction is called dehydrohalogenation.
3. Dehalogenation of vicinal dihalides (dihalogen compounds)
Vicinal dihalides are converted to alkenes by heating with zinc dust in ethyl alcohol.
4. Dehydration of alcohols
Alcohols are heated with sulphuric acid or phosphoric acid at about 443 K. A H2O molecule gets removed from the alcohol giving alkene.
The reaction occurs in multiple steps.
5. Kolbe's electrolytic method (alkenes from salts dicarboxylic acids)
The electrolysis of potassium salts of dicarboxylic acids gives alkenes.
alkynes
alkyl halides
dihalogen derivatives (dihalides)
alcohols
potassium salts of dicarboxylic acids
1. Partial reduction of alkynes
Alkynes can be reduced to alkenes using palladium-charcoal catalyst in catalytic hydrogenation (addition of hydrogen). The reduction (addition of hydrogen) can also be done using sodium in liquid ammonia.
2. Dehydrohalogenation of alkyl halides.
From alkyl halides, an atom of hydrogen and an atom of halogen are removed by treating it with alcoholic KOH.
As a hydrogen atom and a halogen atom are removed from the molecule, the reaction is called dehydrohalogenation.
3. Dehalogenation of vicinal dihalides (dihalogen compounds)
Vicinal dihalides are converted to alkenes by heating with zinc dust in ethyl alcohol.
4. Dehydration of alcohols
Alcohols are heated with sulphuric acid or phosphoric acid at about 443 K. A H2O molecule gets removed from the alcohol giving alkene.
The reaction occurs in multiple steps.
5. Kolbe's electrolytic method (alkenes from salts dicarboxylic acids)
The electrolysis of potassium salts of dicarboxylic acids gives alkenes.
Sunday, January 27, 2008
IIt JEE Revision - Alkynes - Preparation
1. Synthesis of carbon and hydrogen
A stream of hydrogen is passed through electric arc struck between carbon electrodes at 3270 K. Ethyne (acytylene) is obtained.
2. From acetylene (ethyne)
Higher alkynes are prepared from ethyne (acytylene) by treating its sodium salt with alkyl halide. Sodium salt of ethyne is prepared from the reaction of ethyne and sodamide (NaNH2).
Sodium salt obtained from ethyne and sodamide is Sodium acetylide (HC≡CNa).
If methyl bromide is added to it, propyne is obtained.
If ethyl bromde is added to it, But-1-yne is obtained.
As higher and higher alkyl bromide are added higher alkynes are obtained in this process.
3. Action of zinc on tetrahalogen derivatives of alkanes
On treatment with zinc, tetrahalides get dehalogated (eliminated from the molecule) and triple bonds forms and alkyne is obtained
1,1,2,2-tetrabromoethane + zinc --> ethyne +zinc bromide
4. Dehydrohalogenation of vicinal dihalides
Vicinal dihalides (having halogen atoms on the adjacent carbon atoms) get dehalogenated on treatment with alcoholic solution of potassium hydroxide.
5. By electrolysis of aqueous solution of potassium salt of fumaric acid
Fumaric acid is a dicarboxylic acid.
Electrolysis of acqueous solution Potassium fumerate gives ethyne
6. Action of water on calcium carbide
CaC2 + 2H2O gives ethyne and Calcium hydroxide
Calcium carbide required is obtained by heating calcium oxide (from limestone) and coke in an electric furnace at 2275 K.
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1. Dehydrohalogenation of vicinal dihalides
The process takes place in two stages.
In stage I KOH(alc) reacts with vicinal dihalide and vinylic halide is formed.
second stage: Vinyl halide is unreactive and hence vigorous conditions are required and a strong base NaNH2 (sodamide) is used in the reaction to produce the corresponding alkyne.
2. Reaction of metal acetalides with primary alkyl halides. This method can be used to generate large alkyne from the smaller one.
Secondary and tertiary halides cannot be used because eliminatin is the predominant reaction which results in the formation of alkenes.
3. Hydrolysis of CaC two and Mg two C three.
Calcium carbide in reaction with water gives ethyne and calcium hydroxide.(came in X class)
Magnesium carbide in reaction water gives propyne and magnesium hydroxide.
4. Kolbe's Electrolytic Method:
The electrolysis of an acqueous solution of potassium salt of an unsaturated dicarboxylic acid forms alkyne
5. Dehalogenation of vic-tetrahalogen compounds
Tetrahalogenated alkane in reaction with zinc with ethyl alcohol as catalyst gives alkyne and zinc halide.
Preparation of Acetylene or Ethyne
1. By the action of Alcoholic Potash on Ethylene Bromide
BrH two C - CH two Br + 2KOH = C Two H Two + @KBr + 2 H two O
At the end of first state vinyl bromide is formed.
2. By heating tetra-bromoethane with Zinc
C-two H-two Br-four +2Zn = C-two H-two + 2ZnBr-two
3. By the electrolysis of Acqueous solution of Potassium salts of maleic acid (Kolbe's method)
4. By the action of water on calcium carbide (already covered earlier)
5. By heating Iodoform with silver powder
2HCI-three + 6Ag = C-twoH-two + 6AgI
6. By partial oxidation of Methane
2CH-four + 3[O] = C-twoHtwo + 3H-two O
7. By direct synthesis of carbon and hydrogen (Berthelot's synthesis)
2C + H-two = C-twoH-two
------------------------------------------------------------------
1. Action of water on calcium carbide
2. Dehydrohalogenation of vicinal dihalides
3. Action of zinc on tetrahalogen derivatives of alkanes
4. From acetylene
5. By electrolysis of aqueous solution of potassium salt of fumaric acid
6. Synthesis of carbon and hydrogen
Industrial preparation
Ethyne is prepared on an industrial scale by treating calcium carbide with water.
A stream of hydrogen is passed through electric arc struck between carbon electrodes at 3270 K. Ethyne (acytylene) is obtained.
2. From acetylene (ethyne)
Higher alkynes are prepared from ethyne (acytylene) by treating its sodium salt with alkyl halide. Sodium salt of ethyne is prepared from the reaction of ethyne and sodamide (NaNH2).
Sodium salt obtained from ethyne and sodamide is Sodium acetylide (HC≡CNa).
If methyl bromide is added to it, propyne is obtained.
If ethyl bromde is added to it, But-1-yne is obtained.
As higher and higher alkyl bromide are added higher alkynes are obtained in this process.
3. Action of zinc on tetrahalogen derivatives of alkanes
On treatment with zinc, tetrahalides get dehalogated (eliminated from the molecule) and triple bonds forms and alkyne is obtained
1,1,2,2-tetrabromoethane + zinc --> ethyne +zinc bromide
4. Dehydrohalogenation of vicinal dihalides
Vicinal dihalides (having halogen atoms on the adjacent carbon atoms) get dehalogenated on treatment with alcoholic solution of potassium hydroxide.
5. By electrolysis of aqueous solution of potassium salt of fumaric acid
Fumaric acid is a dicarboxylic acid.
Electrolysis of acqueous solution Potassium fumerate gives ethyne
6. Action of water on calcium carbide
CaC2 + 2H2O gives ethyne and Calcium hydroxide
Calcium carbide required is obtained by heating calcium oxide (from limestone) and coke in an electric furnace at 2275 K.
--------------------
1. Dehydrohalogenation of vicinal dihalides
The process takes place in two stages.
In stage I KOH(alc) reacts with vicinal dihalide and vinylic halide is formed.
second stage: Vinyl halide is unreactive and hence vigorous conditions are required and a strong base NaNH2 (sodamide) is used in the reaction to produce the corresponding alkyne.
2. Reaction of metal acetalides with primary alkyl halides. This method can be used to generate large alkyne from the smaller one.
Secondary and tertiary halides cannot be used because eliminatin is the predominant reaction which results in the formation of alkenes.
3. Hydrolysis of CaC two and Mg two C three.
Calcium carbide in reaction with water gives ethyne and calcium hydroxide.(came in X class)
Magnesium carbide in reaction water gives propyne and magnesium hydroxide.
4. Kolbe's Electrolytic Method:
The electrolysis of an acqueous solution of potassium salt of an unsaturated dicarboxylic acid forms alkyne
5. Dehalogenation of vic-tetrahalogen compounds
Tetrahalogenated alkane in reaction with zinc with ethyl alcohol as catalyst gives alkyne and zinc halide.
Preparation of Acetylene or Ethyne
1. By the action of Alcoholic Potash on Ethylene Bromide
BrH two C - CH two Br + 2KOH = C Two H Two + @KBr + 2 H two O
At the end of first state vinyl bromide is formed.
2. By heating tetra-bromoethane with Zinc
C-two H-two Br-four +2Zn = C-two H-two + 2ZnBr-two
3. By the electrolysis of Acqueous solution of Potassium salts of maleic acid (Kolbe's method)
4. By the action of water on calcium carbide (already covered earlier)
5. By heating Iodoform with silver powder
2HCI-three + 6Ag = C-twoH-two + 6AgI
6. By partial oxidation of Methane
2CH-four + 3[O] = C-twoHtwo + 3H-two O
7. By direct synthesis of carbon and hydrogen (Berthelot's synthesis)
2C + H-two = C-twoH-two
------------------------------------------------------------------
1. Action of water on calcium carbide
2. Dehydrohalogenation of vicinal dihalides
3. Action of zinc on tetrahalogen derivatives of alkanes
4. From acetylene
5. By electrolysis of aqueous solution of potassium salt of fumaric acid
6. Synthesis of carbon and hydrogen
Industrial preparation
Ethyne is prepared on an industrial scale by treating calcium carbide with water.
Saturday, January 26, 2008
IIT JEE Revision Benzene Preparation
Preparation of benzene and other aromatic compounds or arenes
1. From alkynes: acetylene and other alkynes polymerise at high temperatures to give benzene and other arenes.
3C2H2 gives C6H6
Benzene was first synthesized by Berthelot by passing acetylene through red hot iron tube.
2. From aryl halides:
Benzene is obtained from chlorobenzene by reducing it with Ni-Al alloy in the presence of sodium hydroxide
Arenes are obtained by reaction fo aryl halide, sodium metal and alkyl halide in dry ether.
Bromobenzene + sodium + Ethylbromide give Ethylbenzene and Sodiumbromide
3. Arenes from Benzene and alkyl halides
Arenes can also be obtained from benzene and alkyl halides in the presence of anhydrous aluminium chloride. This is called Friedel Craft's reaction.
4.From Grignard reagent (Phenyl magnesium halide)
Arenes are also prepared by reacting aromatic Grignard reagent and alkyl halide.
5. From phenol: by distillation of phenol with zinc.
6 Decarboxylation of aromatic acids: by heating sodium benzoate with soda lime. Decarboxylation: Removal carboxyl group
7. From diazonium salts: Benzene diazonium is reduced by hypophosphorus acid.
1. From alkynes: acetylene and other alkynes polymerise at high temperatures to give benzene and other arenes.
3C2H2 gives C6H6
Benzene was first synthesized by Berthelot by passing acetylene through red hot iron tube.
2. From aryl halides:
Benzene is obtained from chlorobenzene by reducing it with Ni-Al alloy in the presence of sodium hydroxide
Arenes are obtained by reaction fo aryl halide, sodium metal and alkyl halide in dry ether.
Bromobenzene + sodium + Ethylbromide give Ethylbenzene and Sodiumbromide
3. Arenes from Benzene and alkyl halides
Arenes can also be obtained from benzene and alkyl halides in the presence of anhydrous aluminium chloride. This is called Friedel Craft's reaction.
4.From Grignard reagent (Phenyl magnesium halide)
Arenes are also prepared by reacting aromatic Grignard reagent and alkyl halide.
5. From phenol: by distillation of phenol with zinc.
6 Decarboxylation of aromatic acids: by heating sodium benzoate with soda lime. Decarboxylation: Removal carboxyl group
7. From diazonium salts: Benzene diazonium is reduced by hypophosphorus acid.
IIT JEE Revision Preparation of Amines
1. Ammonolysis
Hoffmann’s method: When an aqueous or alcoholic solution of ammonia is heated with an alkyl halide at 373 K in a sealed tube, a mixture of three amines (primary, secondary and tertiary) is obtained. It is very difficult to separate the mixture.
2. Gabriel phthalimide synthesis
In this synthesis, phthalimide is treated with alcoholic KOH to give potassium phthalimide.
Potassium phthalimide is treated with alky halide to form N-alkyl phthalimide.
The hydrolysis of N-alkyl phthalimide with 20% HCl under pressure or refluxing with NaOH gives primary amine.
This method can be used for preparing only primary amines.
3. Reduction of nitriles (cyanides)
Nitriles can be reduced to corresponding amines using H2/Raney Li or Pt, LiAlH4 or Na, C2H5OH
When sodium and alcohol are used, the reaction is called Mendius reaction
4. Reduction of isonitriles (isocyanides)
Isonitriles can be reduced to secondary amines using H2/Raney Li or Pt, LiAlH4 or Na, C2H5OH
5. Reduction of amides (Hoffman degradation method)
Amides on treatment with Br2 and KOH give primary amines. The amine formed contains one carbon atom less than the parent amide.
6. Reduction of oximes
Oximes are obtained from aldehydes and ketones by reaction with hydroxylamine. The oximes of aldehydes or ketones can be reduced to primary amines with either Na/CH2H5OH or LiAlH4.
7. Reductive amination of aldehydes and ketones
Reaction between aldehydes or ketones and ammonia results in the formation of imines. Imines are reduced to primary amines with H2, Ni.
Hoffmann’s method: When an aqueous or alcoholic solution of ammonia is heated with an alkyl halide at 373 K in a sealed tube, a mixture of three amines (primary, secondary and tertiary) is obtained. It is very difficult to separate the mixture.
2. Gabriel phthalimide synthesis
In this synthesis, phthalimide is treated with alcoholic KOH to give potassium phthalimide.
Potassium phthalimide is treated with alky halide to form N-alkyl phthalimide.
The hydrolysis of N-alkyl phthalimide with 20% HCl under pressure or refluxing with NaOH gives primary amine.
This method can be used for preparing only primary amines.
3. Reduction of nitriles (cyanides)
Nitriles can be reduced to corresponding amines using H2/Raney Li or Pt, LiAlH4 or Na, C2H5OH
When sodium and alcohol are used, the reaction is called Mendius reaction
4. Reduction of isonitriles (isocyanides)
Isonitriles can be reduced to secondary amines using H2/Raney Li or Pt, LiAlH4 or Na, C2H5OH
5. Reduction of amides (Hoffman degradation method)
Amides on treatment with Br2 and KOH give primary amines. The amine formed contains one carbon atom less than the parent amide.
6. Reduction of oximes
Oximes are obtained from aldehydes and ketones by reaction with hydroxylamine. The oximes of aldehydes or ketones can be reduced to primary amines with either Na/CH2H5OH or LiAlH4.
7. Reductive amination of aldehydes and ketones
Reaction between aldehydes or ketones and ammonia results in the formation of imines. Imines are reduced to primary amines with H2, Ni.
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